Ink jet inks are provided, in particular to smear resistant inkjet inks, and even more particularly to smear resistant pigmented inkjet inks containing polyurethane dispersions that have a glass transition temperature Tg of greater than −30° C. to less than 35° C. and at to least one of the following thermal properties 1) loss modulus E″ of 1.7 to 5×108 pascals, and 2) peak tan delta is 0.23 to 0.65. The pigments used are self dispersed pigments.
Both dyes and pigments have been used as colorants for inkjet inks. While dyes typically offer superior color properties compared to pigments, they tend to fade quickly and are more prone to rub off. Inks comprising pigments dispersed in aqueous media are advantageously superior to inks using water-soluble dyes in water-fastness and light-fastness of printed images.
Pigments suitable for aqueous inkjet inks are in general well-known in the art. Traditionally, pigments were stabilized by dispersing agents, such as polymeric dispersants or surfactants, to produce a stable dispersion of the pigment in the vehicle. More recently though, so-called “self-dispersible” or “self-dispersed” pigments (hereafter “SDP”) have been developed. As the name would imply, SDPs are dispersible in water without dispersants.
SDPs are often advantageous over traditional dispersant stabilized pigments from the standpoint of greater stability and lower viscosity at the same pigment.
Although advantageous in some regards, penetrating pigment-based ink compositions may cause the color development to be somewhat poor when ink is printed on plain paper. Increasing the content of the pigment may improve color development but it generally also increases the viscosity of ink and thus is often unfavorable for the ejection stability of ink. However, the beneficial properties of SDPs allow these pigments to be loaded to higher levels with less impact on viscosity. Thus a penetrating ink having excellent color development is still possible by using SDPs.
Despite these potential advantages to the use of SDPs, inks formulated with SDPs tend to be somewhat poor in fixation on recording media, in particular plain paper. An example of poor fixation is when an ink is smeared when a highlighter pen is brushed across the inkjet printed image.
Still, there is need for dispersion stable, ejection stable inkjet inks comprising an SDP which can print with good color on plain paper and which are smear resistant.